Ship positioning means and method



Nov. 28, 1961 W. R. POSTLEWAITE SHIP POSITIONING MEANS AND METHOD Filed Dec. 24, 1958 4 Sheets-Sheet l INVEN TOR WILLIAM R. POSTLEWA/TE ATTO N EYS Nov. 28, 1961 w. R. POSTLEWAITE 3,

SHIP POSITIONING MEANS AND METHOD Filed Dec. 24, 1958 4 Sheets-Sheet 3 FIG.7 FIG.1OA FIG.1OB

RECEIVER u SELSYN 174 AMPLIFIER INCLINATION I66 182 180 l POWER DEPTH I V RECEIVER SUPPLY 155 l SELSYN l f' l TRANSMITTER SELSYNS l l I AMPLIFIER-NCLINATION L 1 INVENTOR WILLIAM R. POSTLEWA/TE FIG. 5 J Y ,J

Nov. 28, 1961 w. R. POSTLEWAITE SHIP POSITIONING MEANS AND METHOD 4 Sheets-Sheet 4 Filed Dec. 24, 1958 all," W I I'll H I" m I'I'I'I'I'll'"! N N E m m n T T A A m N H N E l T I a 4 L 0? 6 L R 7 C 8 E 7 C S I m (ID 11 m E VR M m a III I 2 L M R W R ER R 8 Y E W P 5 B H 0U F 2 u 5. u P P 6 M M 5 2 A A 4 5 Z G 1 "CG" 1.. ND Al 6 n: w. L 7- lllll L. l BALANCING BRIDGE FIG.11

STRAIN GAUGES ATT NEYS United States Patent 3,010,214 SHIP POSITIONING MEANS AND METHOD William R. Postlewaite, Menlo Park, Calif., assignor to California Research Corporation, San Francisco, Calif., a corporation of Delaware Filed Dec. 24, 1958, Ser. No. 782,837 6 Claims. (Cl. 33-215) This invention relates to an offshore drilling operation and more particularly to means for determining the position on the surface of the water of a floating drilling vessel relative to a well bore drilled into the submerged land. The invention has particular pertinence to a means for positioning, and maintaining the position of, a floating drilling vessel vertically above a submerged well bore to avoid bending unduly the rotary drill string which extends downwardly from the drilling vessel into the well bore.

In one procedure for accomplishing offshore drilling, a floating drilling vessel is anchored at the surface of the water above a submerged well site, and a well is drilled from it into the underlying land. The drilling operation is accomplished by extending a drill string and bit downwardly from the floating vessel into contact with the submerged land surface and thence rotating the drill string by means aboard the vessel.

In pursuance of this drilling operation, the drill string is exposed in the water and forms the principal connection between the drilling vessel and the submerged well bore. Therefore, it is exposed to subsurface water currents which impose a lateral force on it which tends to produce a lateral displacement of the portions of the drill string between its supported ends. During the initial drilling operation, when the drill string and bit are first lowered from the drilling platform toward the underwater bottom, these lateral forces may cause the lower end of the drill string to be displaced from the vertical relative to the drilling vessel. Thus the drill string assumes a curved configuration through the water, which it Will maintain when the drill bit bores into the submerged earth. As the well bore is deepened, the added weight of the drill string increases the tensile stresses in the curved portion of it and ultimately leads to a condition where fatigue stress caused by reverse flexure of the rotating drill pipe, or other stresses, will cause the drill string to fail.

Other conditions of open water drilling also can lead to the circumstance of a drill string being operated while it is curved or bent between the submerged well bore and the drilling vessel. For example, a floating drilling vessel anchored by catenary cables in the usual manner will periodically be displaced from its initial position through the action of wind and tidal forces. In the normal course of events, such a displacement may amount to or more feet on either side of the vertical from the well bore. This lateral displacement may prove critical when the depth of the well is such that the weight of the drill string in the well bore causes the portion of the drill string exposed in the water to be operating under.

high tensile stresses. The problem is magnified when the drilling vessel is exposed to storm forces which cause the 3,010,214 Patented Nov. 28, 1961 in a substantially straight line extending from the drilling vessel to the submerged well bore. Thus, breakage of the drill string due to flexure or fatigue stresses caused by rotating it while in a bent configuration would be eliminated.

It is an object of this invention to provide a novel means for determining the position on the surface of the water of a floating drilling vessel relative to a submerged well bore.

A further object of this invention is to provide means for accomplishing an offshore drilling operation from a floating drilling vessel while maintaining the drill stringin a substantially straight line throughout a portion extending from the drilling vessel through a body of water and into a submerged well bore.

Another object of this invention is to provide novel apparatus for determining the variations in degree and direction of the angular displacement from the vertical of a flexible member extending from a floating vessel at the surface of the water into submerged wellhead equipment fixed adjacent the underwater bottom.

Other objects will become apparent as the description of the invention proceeds hereinafter.

The objects of this invention are achieved through apparatus which is lowered along the exterior of a submerged drill string while the azimuthal orientation of the apparatus is maintained constant. The apparatus is traversed along the drill string from the surface of the water to the bottom, and the deviation of the drill string from the vertical is determined as a function of elevation. By this method the location of the points of the greatest curvature of the drill string, and hence the points where failure is most likely to occur, as well as the direction of deviation from the vertical, can be located. The floating vessel is moved in position to relieve the curvature of the drill string and thus prevent the failure of the latter.

The following specification, together with the accompanying drawings which form a part of it, describes several modifications of apparatus for accomplishing the objects of this invention, particularly as applied to a fully floating drilling vessel.

With reference to the drawings:

FIG. 1 illustrates in side elevation, with portions of the drilling vessel broken away to reveal the disposition of apparatus Within the hull,'an arrangement of parts in accordance with this invention being usedduring an oifshore drilling operation.

FIG. 2 illustrates in side elevation and partly in section an apparatus for determining the degree and direction of deviation of a drill string from the vertical.

FIG. 3 is a plan view of portions of theapparatus taken along the line 33 of FIG. 2.

FIG. 4 is a plan view of the detail of the apparatus taken along the line 44 of FIG. 2. 1

FIG. 5 is a schematic representation of the electrical connections between elements of the apparatus illustrated in FIG. 2.

FIG. 6 illustrates in side elevation and partly in section a modification of apparatus employed in this'invention.

FIG. 7 represents a plan view of a portion of the apparatus taken along the line 77 of FIG. 6, and illustrates the functioning of a centering device for it.

FIGS. 8 and 9 represent, partly in section, details of the apparatus illustrated in FIG. 7, and show the opera tion of portions of the centering device when engagin enlarged sections of the drill string.

FIGS. 10A and 10B illustrate in side elevation and partly in section details of the operation of thelapparatus illustrated in FIG. 7. v V

FIG.- 11 is a schematic representation of the electrical connections between elements of the apparatusiillustrated in FIG, '6- and further illustrates the mariner,inwhich these elemeI1I are CQHnected to remote recording equipment.

Referring to the drawings, and particularly to FIG. 1, there is illustrated an ofishore drilling vessel 20 which is anchored at the surface 22 of a body of water above a submerged well site 24 by a plurality of anchor lines. A drill string 26 is supported in a derrick 28 aboard the drilling vessel and extends downwardly through a rotary table 30 'to a submerged wellhead 32 which caps a Well bore being drilled into the submerged earth.

In the method of ofishore drilling illustrated, the drill string is pulled downwardly from the drilling vessel to the wellhead by a pair of t-owlines 34 and 36. These lines, are reeled on respective winches 38 and 40 which are positioned adjacent the edge of a trunk 42 formed through the hull of the vessel and thence extend downwardly through the water to respective sheaves 44 and 46 mounted on radial arms extending from the wellhead. The towlines are mounted over their respective sheaves and thence are connected to a towing head 48 which can be raised and lowered through the water.

7 Initially, the towing head is at the surface and is detachably connected to the lower end of the drill string 26. The winches are then operated to pull the towing head and the attached drill string downwardly through degree and direction of deviation of the drill string from V the vertical in relation to depth below the water surface. As illustrated in FIG. 2, this apparatus comprises a generally cylindrical carriage element 52 which has an axial passage 54 extending through it to receive a string of drill pipe 26 in sliding relationship. The carriage element is bell ended, as at 56 and 58, to provide chambers of increased internal diameter in the end portions. A centering device is mounted within each bell-ended portion to bear against the string of drill pipe and to maintain the cylindrical carriage element 52 in coaxial relationship with it as the apparatus is moved axially along the drill string. a

T The bell end 56 supports a centering device 60 which 'hastradially inwardly directed resilient fingers 62, and the bell end 58 supports a similar centering device 64 containing radially inwardly directed resilient fingers 66. When 'an end of the carriage element 52 surrounds a section of the drill pipe of uniform diameter, the resilient V fingers of the centering device extend to bear uniformly around the circumference of the drill pipe. They exert sufficient pressure to maintain the'associated end of the carriage element 52 in coaxial relationship with the drill pipe as the latter revolves, or as the cylindrical element is moved along the drill'pipe in an axial direction. This condition is illustrated by the bell end 58 and the complementary'centering device 64. FIG. 4 illustrates in plan view the relationship of the parts in the circumstance described immediately heretofore.

When the carriage element encounters a tool joint'or other portion of enlarged diameter on the exterior'surconcentric with it, Thusyas illustrated at the bell end 56 of FIG. 2, the resilient fingers62 of the centering device 60 bend to accommodate the increased external diameter coaxial relationship of this .end of the carriage element 52 as it rides over the interconnected pipe sections.

In this modification of the invention, preferably the carriage element, together with the centering devices, are made in half-sections which can be assembled around a continuous drill string and then fastened together in a rigid manner. Each centering device is made of a rubher-like material, such as a synthetic rubber or a natural rubber, each half-section of which is secured to a corresponding backing plate in a unitary manner. The backing plates fit within and are afiixed to the chamber of the complementary bell-ended section.

Thus, as best seen in FIG. 4, the centering devices 60 and 64 are formed of two half-sections 70 and 72, each of which is affixed to a respective backing plate 74 and 76 of semicylindrical form. The backing plates, and hence the half-sections of the centering device, are secured within the appropriate complementary bell-ended portions of the half-sections of the carriage element 52 by fastening means, such as screws 78. Desirably, when the halfsections 80 and 82 of the carriage element are secured together, a locking ring 84 is assembled with or sprung into the inner circumferential groove 86. formed'in the chambers of each of the bell-ended sections to assist in maintaining the half-sections of the centering device in mutual alignment and to aid in securing the centering device to the carriage element. This structure permits the centering devices on a particular carriage element to be replaced'when they become worn, and also permits centering devices of the optimum. internal diameter to be inserted in the apparatus to accommodate a particular size of drill pipe. 7 7

Each half-section 80 and 82 of the carriage element has a respective transversely disposed plate member 88 and 90 rigidly afiixed to and extending radially from it. Respective cylindrical guide collars 92 and 94 are afiixed to the radially outer ends of the plate members to receive corresponding guidelines 34 and 36 in sliding relationship. Strengthening skirts 96 are disposed around the periphcry of each plate member and are fastened to it and the connected guide collar in a unitary mannerr Additional strengthening webs 98 and 100 are secured to each plate member and its connected half-section of the carriage element. Respective complementary lugs'102 and 104 projecting from adjacent mating portions of the plate members 88 and 90 provide a means for bolting these sections together. Other complementary mating lugs,

, such as 106 and 108, are placed at intervals on each side or the drill string adjacent the joint 68. The centering posing circum ferentia'lly disposed fingers to i maintain the *device' is designed to provide asymmetrical fle'xure'of op of the carriage element 52 along the cleavage plane of the half-sections and 82 toprovide a further means for securing these sections together to accomplish a rigidly connected assembly. Similarly, the guide collars 92 and 94 are madein half-sections which can be assembled around the respective guidelines and then fastened together by complementary lugs 110 and 1-12 ina unitary manner.

Each plate member 88 and has a chamber or receptacle, 114 and 116, respectively, rigidly-secured to it. A pendulum is mounted in each chamber on a substantially horizontal axis, and the axisof the pendulumin one chamber is disposed at 90 to the axis, of the other pendulum. Thus the carriage eleme'nt'52 willbe dis placed relative to one or the other, or both, pendulums if it is inclined from the vertical; I

The pendulum 118 in chamber 114 is securely fastened to an axle 120, as by a tightly fitted'pin 122. The axle is mounted on antifriction bearings 124 and 126. which are attached to a cover member .128 by a bracket arrange ment 130. The. axle is disposed 'in a radial plane pro5 jected from the longitudinal axis of the cylindrical carriage element 52', and the pendulum is constrained to relative swinging movement a direction transversely of thisplane. '7 I The axle is connected through a backlash-free flexible coupling 132 to a-selsyn 134 which alsois attached to the cover 128 in coaxial alignment with the axle 120. The cover 128 is secured to the top of the chamber 114 in a fluid-tight manner, as by a plurality of bolts 136, to exclude the ambient water from the chamber. A damping liquid 138 fills the bottom of the chamber 114, and the lower portion of the pendulum 118 is immersed in the damping liquid when the various elements of the device are assembled for operation.

Similarly the pendulum 140 in the chamber 116 is rigidly connected to an axle 142 mounted on antifriction bearings connected to the cover 144 in the manner of the axle 120 for the complementary pendulum arrangement described heretofore. However, this axle 142 is disposed transversely of the radial plane in which the axle 120 is disposed, and the pendulum 140 is constrained to relative swinging movement in a direction parallel to this plane. The axle 142 is connected through a flexible coupling 146 to the axially aligned selsyn 148 which also is afiixed to the cover 144. The cover is secured to the top of the chamber 116 in a fluid-tight manner, and the chamber contains a damping liquid in the manner described heretofore with respect to the chamber 114.

Insulated electrical conductors 149 from the selsyn 148 are led through a water-tight packing gland 150 on the cover 144 and thence to an electric-a1 connector 152 which is mounted on the carriage element 52 at its cleavage plane. The electrical conductors are continued from the connector 152 to a water-tight T fitting 154 secured to the cover 128. The connector is made to separate when the two half-sections 80 and 82 of the carriage element are displaced apart, and to reconnect the portions of the insulated electrical conductors when the half-sections are assembled together. The connector is constructed to exclude water when its portions are assembled together.

Insulated electrical conductors 155 from the selsyn 134 also are led through the Water-tight T fitting 154, and both sets of conductors are included in a cable 156 which connects the transmitter selsyns 134 and 148 with respective receiver selsyns aboard the drilling vessel. This cable includes a tensile member, such as a reinforced wrapping or a flexible wire line, and serves as a loadcarrying means for raising and lowering the carriage element and the pendulum apparatus mounted on it along the drill string. A counterweight 157 is provided adjacent the radially outer end of plate member 88 to counterbalance the eccentric loading of the cable pull on the assemblage 50.

The cable 156 is wound on a winch 158 aboard the drilling vessel, and the electrical conductors are connected through a rotary connector 160 to a recording mechanism 162. Preferably the cable 156 is attached to a split guide sleeve 164 which is assembled around and runs along one of the towlines, as line 34, as the apparatus is lowered or raised through the water to prevent the cable 156 from becoming entangled with other submerged portions of the apparatus. 7

Referring now to FIG. 5, the transmitter selsyns 134 and 148 are connected through the electrical conductors 155 and 149 and the rotary connector 160 with corresponding receiver selsyns 166 and 168 mounted on the drilling vessel, preferably in the console assembly 162. The receiver selsyns are connected to respective amplifiers 170 and 172, and each amplifier is connected to a respective recording device, which in the schematic illustration represented takes the form of meters 174 and 176.

Preferably, these meters are calibrated to indicate the angular displacement fromthe vertical of the axis of the drill string -at the location of the pendulum assemblage. A measuring device 178 is operatively connected to the cable 156 to determine the length of cable let off from the winch 158. This device operates the meter .180 which indicates the depth below the surface selsyn systems, the amplifiers and the appurtenant equipment.

It will be appreciated that the recording device may, if desired, be combined and take the form of a chart upon which will be traced continuous graphs which represent the variations of the signals generated by the transmitter selsyns with relation to the depth of the indicating device below the surface of the water, or the signals may be combined vectorially to produce a resultant indication of the parameters of the deviation, or some other convenient form of recording mechanism known to the art may be used.

FIG. 1 illustrates the apparatus described heretofore assembled on a drill string during an oifshort drilling operation. As illustrated, the drilling vessel is displaced from a truly vertical relationship with the well bore, and as a result the drill string is curved through the water between the wellhead 32 and the rotary table 30. The lateral displacement of the vessel imposes serious bending stresses in the drill pipe. For example, when drilling to 4,000 feet with 3 /2 0D. 9.3 lb.-per-foot steel drill tubing in 200 feet of water, a displacement of the drilling vessel 10 feet in a lateral direction from the vertical extension of the well bore can create reverse bending stresses in the range of 50,000 pounds per square inch. This is in addition to an axial tensile stress of 14,000 pounds per square inch, and bending stresses of approximately 8,000 pounds per square inch due to ship roll and the drag of ocean currents on the drill pipe. Thus it is important that the drilling vessel be held within the limits of a narrow range of lateral displacement to avoid exceeding the yield point or the fatigue limit of the steel tubing. These limits may be determined from appropriate tables or charts, which relate the parameters of tensile stress and permissible drill pipe curvature to Water depth and lateral displacement of the vessel, for the various drill pipes used.

In accordance with this invention, the device described heretofore is lowered along the drill string from the surface of the water to the bottom, and a record of angular deviation of the drill string from the vertical with respect to depth is obtained. The pendulum assemblages are held in a known azimuthally oriented position by the towlines 34 and 36. A permanent magnet 183 may be secured to the wellhead apparatus to assist in determining the compass orientation of the lower ends of the towlines by an auxiliary instrument run down the drill string. Hence the amount and direction of angular deviation of the drill string from the vertical at a given depth is determined by combining vectorially the relative swing of each pendulum with respect to the longitudinal axis of the drill string at that depth. Thus in FIG. 2, for example, the pendulum assemblage is maintained oriented in the plane of the paper by the towlines. The axis of the drill string 26 is displaced relative to the pendulum in a direction to indicate a deviation from the vertical in the plane of the paper in the direction illustrated. Likewise, the pendulum 118 will indicate a displacement of the drill string from the vertical in the direction normal to the plane of the paper.

When these relative displacements are combined vectorially, the amount and direction of the deviation is determined. Thus the portion of the drill string which is operating under the largest reverse bending stress can be located, and the amount of the stress can be determined from the angular displacement from the vertical of the length for an initial position of the vessel and for a subsequent position, and determining the difference.

When the curvature of the drill string exceeds the amount which permits the safe operation of the drilling apparatus, .the anchored position of. the drilling vessel is drill string may have.

7 changed to bring it more closely in alignment with the vertical extension of the axis of the well bore. As indicated in FIG. 1, desirably the respective control switches 184, 186, 188 and 190 for the individual winches, as represented by the winch mechanism 192, which are connected to the respective anchor lines 194, 196, 198 and 200 are mounted in the console 162 which contains the recording meters described heretofore. With the pendulum assemblage maintained at the elevation of critical curvature of the drill string, the appropriate winches are operated to move the drilling vessel in its anchored position in a direction to relieve the curvature in the drill string. Thus, for example, if the condition exists as illustrated in FIG. 1, the winches connected to the forward anchor lines 194 and 196 will be operated to reel in line While the winches connected to the stern anchor lines 198 and 200 will be operated tounreel line. While this operation is proceeding, the operator observes the recording meters to assure himself thatthe motion of the boat is in the proper direction, and he continues the operation of the winches until the recording meters indicate that the drill string has been brought into vertical alignment with the well bore, or that the excessive amount of curvature has been removed from it.

In one method of operation with the device of this invent-ion, when the drilling vessel is moved to the opti-' mum position to relieve the bending stresses in the drill string, the pendulum assemblage is placed on the drill string at an elevation where the latter will most readily be deviated from the vertical upon a lateral displacement of the drilling vessel. Thus while the drilling operation is proceeding, the driller can by observing the meter dials be informed immediately if the drilling vessel is moved from its optimum position. Obviously the recording arrangement may be equipped with alarms which will give a visual or aural indication when the displacement of the vessel exceeds an allowable limit. f

In an alternative method of operation, the pendulum assembly is detached from the drill string during the normal drilling procedure. Periodically the rotation of the drill string is stopped, and the pendulum assembly is mounted on it and traversed along its length to determine degree and direction of any longitudinal curvature the This latter method eliminates any errors in the indications of the direction of deviation from the vertical of the drill string in circumstances where frictional drag between the rotating drill string and the centering devices of the carriage element 52 may cause an azimuthal displacement of the pendulum assembly against the restraining force of the towlines.

FIG. 6 illustrates a. modification of a device made in accordance with this invention. In the following de scription the same numerals as used heretofore will be employed to indicate corresponding portions of the two embodiments. element 52.is positioned around the drill string 26 and maintained in coaxial alignment with the latter by a plurality ofcastors mounted on its top and bottom ends 202 and. 204, respectively. As illustrated in FIG. 7, preferably there are four castors 206, 208, 210 and 212 at each end of the cylindrical carriage element. The

castors are positioned in pairs in diametrically opposed In this modification a cylindrical carriage axis 220 by an amount X. Both the axle 218 and the swivel axle are mounted in antifriction bearings, and the ofiset distance is chosen to provide a castor assembly which is very responsive to the change of direction of motion of the cylindrical carriage element 52 relative to the drill string. Thus, if the assemblage is held at a stationary position on the drill string while the latter is being rotated, each castor wheel will assume the position indicated in FIG. 10A. However, when the assemblage is traversed along the rotating drill string, the castors immediately will swivel to assume a position to accommodate both the relative rotary and transulatory motion. When the assemblage is traversed along a stationary drill string, the castor Wheels swivel to the position indicated in FIG. 10B.

A transverse plate 222 is affixed to the cylindrical carriage element 52 and extends radially on diametrically opposite sides thereof. A respective guide collar 92 and 94 is attached to each of the radially outer ends of the plate to receive, respectively, the guidelines 34 and 36. Preferably each guide collar is formed of two longitudinal half-sections which can be assembled around a guideline and secured together by bolts 224 or other means. The transverse plate 222 is stiffened by strengthening ribs 96, 98 and 100 in the manner described heretofore with respect to the previously described modification of the invention.

A pair of chambers or receptacles 114' and 116 are secured to the transverse plate 222 with each chamber of the pair disposed on diametrically opposite sides of the cylindrical carriage element 52. Each chamber is closed by a fluid-tight cover 128 and 144, respectively, on the inner side of which is mounted a respective pendulum 226 and 228. The lower portion of each receptacle is filled with a damping liquid 138 through which the pendulunis move.

In this modification of the invention the principal mass 230 of each pendulum, as the pendulum 226, for example, is secured to the lower end of a flat spring 232, the upper portion of which is rigidly affixed to a bracket element 234 secured to the cover 128. The spring is made with suflicient width in relation to thickness to provide rigidity in the direction of its width dimension while readily permitting bending in the direction of its thickness dimension. The pendulum 226 in the receptacle 114 is set at an angle of 90 to the complementary pendulum 228 and receptacle 116. l

A respective strain gauge, 236 and 238, is secured to each pendulum spring in a manner to produce'an electrical signal corresponding to the degree of bending of a the spring to whichit is attached. The electrical conductors 240 and 242 for the strain gauge 238 are led in relationship to engage the circumference of the drill stn'ng withsubstantially' equal force. The periphery of each resilient pressure. The resiliency'of the'tire-permits it to detonate accommodate portions of the drill string of' increased external diarnet'er, such as encountered at the tool joint or other connectors'between pipe sections, as indicated in FIGS. 8 ,and9.

. :As best. illustrated in FIG. 8, the axle21ilor the caster Y H "whee1i214 is offset firom -diriect alignment with the swivel a conduit 244 through a water-tight packing gland 150 affixed to the cover 144 and thence to a water-tight T connector 154 on the cover 128. The electrical conductors 246 and 248 for the strain gauge 236 are led in a conduit 25!) into the water-tight T connector 154, and both pairs of conductors are combined in a cable 156 which is secured to the T connector. The cable electrically connects the pendulum assemblage with recording equipment 162 on the drilling vessel.

The cable 156 includes a' tensile element which provides a means for raising and lowering the pendulum assemblages along the drill string in the manner described heretofore. A counterweight157 is afiixed to the transverse plate 222 to counterbalance the eccentric loading of the cable. g Y

FIG. 11 is a schematicillustrationof the electrical connections between theelements of. this modification of connect the strain gauges'in the comparable respective bridge circuits 252'an'd 254. Thebridge circuits are connectedto respective amplifiers 256 and'258 and. then to 9, corresponding recording devices, such as indicated by the meters 174 and 176. An interconnected power supply 264 supplies the electrical energy for operating this device.

Each bridge circuit includes a variable resistor 266 which permits the circuit to be balanced to give a zero reading on the recording apparatus when the drill string is vertical. When the carriage element 52 is displaced angularly relative to the vertical, the pendulum springs 232 will bend an amount proportional to the component of displacement in the direction of permissible pendulum movement. This bending will create a corresponding electrical signal in the respective strain gauge affixed to each pendulum spring, and the connected meters 174 and 176 will register the component amounts of deviation of the carriage element from the vertical. The total deviation of the drill string from the vertical is, of course, a vector resultant of the two components.

The operation of this modification is similar to that described heretofore. The assemblage 50 is tranversed along the drill string to determine its angular deviation from the vertical at various elevations, which latter are measured by the device 178 and registered on the meter 180. When this deviation indicates the bending stresses in the drill string are excessive, the drilling vessel is moved in its anchored position in a direction to reduce the bending stresses. In this modification of the invention the drill string 26 is inserted through the axial passageway 54 in the cylindrical carriage element 52 while the latter is aboard the drilling vessel. 7 The pendulum assemblage is then lowered through the trunk 42 until the guide sleeves 92 and 94 are positioned adjacent the towlines 34 and 36.- The halves of the guide sleeves are then fastened together, and the device is lowered by cable 156 along the towlines and drill string for submerged operation. When the drill string is raised to change a drill bit, the assemblage 50 is raised along with it until it enters the trunk of the vessel. The guide sleeves 92 and 94 then are disengaged from their respective towlines, and the pendulum assemblage is further raised to the deck of the vessel to make the drill bit accessible. The carriage element 52 may remain mounted on the lower portion of the drill string while the drill bit is being changed and can be lowered into the water when the drill bit is returned to the well bore.

Alternatively, the assemblage 50 can be removed from the drill string until such time as it is desired to run a traverse. With the drill string remaining in the well bore, the top portion of it is supported by the drilling vessel separately from the connection to the derrick and disconnected at a joint above the support. The carriage element is then slipped over the upper end of the drill string, which subsequently is resupported by the derrick. With the drill string remaining stationary, the assemblage 50 is connected to the towlines and the traverse made in a manner similar to that described heretofore.

It is apparent from the foregoing description that the apparatus of this invention achieves the objects as set forth heretofore and provides a means for determining the position of a floating drilling vessel with respect to its vertical alignment with a submerged well bore and for placing the vessel vertically above the Well bore. It is apparent that other modifications than those described herein may be made to the apparatus of this invention without departing from the inventive concept. Therefore, it is intended that the invention embrace all equivalents within the scope of the appended claims.

I claim:

1. Apparatus for use in offshore drilling of well bores comprising in combination a floating drilling platform anchored at the surface of the water above a submerged well site, a string of tubing attached to said drilling platform and extending downwardly through said body of water and into a wellhead submerged at the bottom of said body of water and afiixed to the submerged earth at said well site, a pair of guidelines attached to and extending downwardly from said drilling platform to said wellhead in parallel spaced relationship to each other and to said string of tubing, means to secure the lower ends of the respective guidelines to said wellhead, an elongated carriage slidably mounted on the exterior surface of said string of tubing for movement longitudinally thereof, centering means affixed to said carriage and flexibly engaging the outer circumferential wall of said string of tubing to maintain said carriage in concentric relationship with said string of tubing as-said carriage is moved longitudinally relative to said string of tubing, a pair of guide arms aflixed to said carriage and projecting radially outwardly therefrom toward said pair of guidelines, a respective guide sleeve alfixed to the radially outer end of each of said pair of guide arms and circumferentially surrounding a respective guideline for relative movement longitudinally thereof, a respective housing affixed to each of said guide arms, a respective pendulum mounted in each said respective housing with each pendulum constrained to swing about a substantially horizontal axis and with the said horizontal axis of one said pendulum positioned at right angles to the horizontal axis of the other said pendulum, respective electric signal generating means operatively connected to each said pendulum for producing an electrical signal which is proportional to the relative angular displacement of said respective pendulum with respect to said carriage when said carriage is moved from a vertical position, and recording means onsaid drilling platform and electrically connected to said respective electric signal generating means to record an angular position of said carriage relative to the vertical.

2. Apparatus for indicating the drift of a floating vessel from a position vertically above a site on the submerged land surface comprising a string of tubing extending from a floating vessel downwardly through a body of water and into fixed contact with a submerged site on the land underlying said body of water, a pair of guidelines extending from said vessel downwardly through said body of water in substantially parallel relationship to said string of tubing and with the lower end of said guidelines fixed in position relative to the-said submerged site, an elongated carriage element circumferentially surrounding a portion of said string of tubing and mounted for relative movement longitudinally thereof, centering means mounted on said carriage and resiliently engaging the outer surface of said string of tubing to maintain said carriage in substantially coaxial relationship with said string of tubing as said carriage is moved along said string of tubing, a pair of guide arms fixed to and extending laterally from said carriage and engaging said guideline in a slidable connection, a first chamber carried by said carriage element and rigidly fixed in relation thereto, a first pendulum mounted in said first chamber and constrained to swinging movement in a plane which is parallel to the longitudinal axis of said carriage element, a second chamber carried by said carriage element and rigidly fixed in relation thereto, a second pendulum mounted in said second chamber and constrained to swinging movement in a plane which is parallel to the longitudinal axis of said carriage element and at right angles to the plane of swinging movement of said first pendulum, a damping liquid for said pendulums in each said chamber, a respective fluid-tight cover closing each said chamber, respective electric signal generating means operatively connected to each said pendulum for pro-.

ducing an electric signal which is proportional to the angular displacement from the vertical of the longitudinal axis of said carriage element in the plane of swinging movement of said pendulum, recording'means on said vessel and electrically connected to said respective electric signal generating means on said pendulums to record the angularposition of the longitudinal axis of said carriage element relative to the vertical, means connected to said carriage element and said vessel to raise and lower said carriage element along said string of tubing by ma- 11 nipulation from said vessel, and means for determining the position in elevation of said carriage element on said string of tubing.

3. A device to indicate the angular deviations from the vertical of a string of drill pipe during an offshore drilling procedure comprising a floating drilling vessel anchored on the surface of a body of water, a string of drill pipe extending from said vessel downwardly through said body of water and into a submerged Well bore, an azimuthally oriented guideline extending downwardly from said vessel through said body of water in substantially parallel spaced relationship with said string electric signal generating means actuated by each said pendulum to generate an electrical signal proportional to the component of displacement from the vertical of said carriage assembly in the plane of swinging movement of the respective pendulum, electrical conductors connecting each said signal generating means with recording apparatus on said drilling vessel, and means to lower and raise said carriage assembly along said string of drill pipe and connected to means for measuring the elevation of said carriage assembly below said surface.

4. A device for indicating the amount and elevation of an angular displacement from the vertical of a string of tubing extending downwardly through a body of water comprising a cylindrical element having an axial passage therethrough to receive a string of tubing in sliding relationship, resiliently operative centering means disposed between and in contact with the wall of said passage and theouter wall of said tubing to maintain said cylindrical element in coaxial relationship with said tubing, a transversely disposed member fixed to said cylindrical element and extending radially therefrom on diametrically opposed sides thereof, a respective cylindrical guide collar having an axial passageway therethrough fixed to each radially outer end of said member to receive a respective guideline in sliding relationship, a pair of pendulum drical element, a respective pendulum mounted on a horizontally disposed axis in each said chamber for swinging gravity actuated movement in respective vertical planes which are at right angles to each other, respective means actuated by each of said pendu-lums'to produce electrical signals which are proportional to the angle between the longitudinal axis of said cylindrical element and the vertical, means to move said cylindrical element axially along said string of tubing, and means to record said electrical signals.

5. The method of correcting the drift of a floating vessel from an initial anchored position above a fixed location on the submerged land surface comprising extending an elongated means downwardly from a support on an anchored vessel floating on the surface of a body of water and into laterally fixed engagement with the land submerged'below said body of water, slidably mounting on the exterior of said elongated means a first means for indicating the amount and direction of angular deviations from the vertical along the length of said elongated means, traversing said first means along the length of said elongated means while maintaining a substantially fixed orientation in azimuth of said first means, and moving said vessel to reduce angular deviations from the vertical of said elongated means in accordance with the indications of said first means.

6. A method for determining the amount and direction of drift of a floating vessel from a position above a fixed location in the submerged land comprising extending an elongated flexible means downwardly from a support on a vessel floating on the surface of a body of water and into laterally fixed engagement with the land submerged below said body of water, placing said elongated means in tension between said floating vessel and the underwater bottom, slidably mounting on the exterior of said elongated means a first means for indicating angular deviations from the vertical of said elon References Cited in the file of this patent UNITED STATES PATENTS Savitz Feb. 4, 1947 Nicolson Oct. 15, 1957 

